Hybrid frp-concrete-steel double-skin tubular beams and hybrid dstb/slab units using the beams

ABSTRACT

This invention relates to a novel hybrid FRP-concrete-steel double-skin tubular beam and a hybrid beam/slab unit which employs the hybrid tubular beam. The hybrid double-skin tubular beam consists of an outer FRP tube, an inner steel tube, and concrete filled between the outer FRP tube and the inner steel tube, and the inner steel tube is provided with a plurality of shear connectors on its side engaged with concrete. The inner steel tube is located eccentrically relative to the outer FRP tube towards the side of the hybrid tubular beam to be tensed. The inventive hybrid beam/slab unit is a slab-on-girder system which is comprised of the hybrid double-skin tubular beam and the lightweight slab of good corrosion resistance (such as a FRP slab or an aluminum slab) that is provided thereon, or a deck or floor system which is comprised of the hybrid double-skin tubular beam and a FRP-rib reinforced concrete slab and in which the upper portion of the hybrid double-skin tubular beam is engaged with the bottom of the FRP-rib reinforced concrete slab thereinside so as to form an integrated body. The inventive hybrid tubular beam features an excellent resistance against corrosion, a good ductility and cost-effectiveness. and is lightweight, while at the same time allows for easy construction and connection with other members.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Chinese Patent Application No. 201010180716.6 filed on May 24, 2010, the entire content of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The invention relates to loaded members in bridge and construction structures, and particularly, relates to hybrid FRP-concrete-steel double-skin tubular beams (DSTBs) and hybrid DSTB/slab units using the hybrid beams.

BACKGROUND OF THE INVENTION

Popular beam forms that are currently widely employed in bridge and construction structures include reinforced concrete (RC) beams and steel beams. Undesirably, both beam forms are prone to deteriorating and corrosion in harsh environments, such as in the wild, at the seaside or in a humid environment. In other words, these beam forms suffer from poor corrosion resistance.

Recently, fibre-reinforced polymer (FRP) composites have been increasingly widely employed for the purpose of solving deterioration and endurance issues that would otherwise occur in bridge and construction structures worldwide. FRP is a novel nonmetal material that is composed by mixing fibers of high performance, such as carbon fibers, glass fibers and Basalt fibers, with resin matrix and then compounding the mixture through a certain process. As a material with high corrosion resistance, FRP possesses additional advantages of lightweight, high strength, and easiness for moulding.

Prior art beam forms that employ FRP include: (a) all-FRP beams (referred to as type I beams hereinafter) which commonly resume forms resembling those of steel beams (such as I-shaped or box-shaped beams), (b) hybrid beams incorporating FRP and concrete, such as FRP bar-reinforced concrete beams, hybrid beams composed of an FRP profile that functions to bear tension and a concrete layer cast thereon that functions to bear compression, and concrete-filled FRP tubes (hereafter referred to as type II beams, type III beams and type IV beams, respectively). The above-mentioned beam forms suffer from high costs due to the use of a large amount of FRP material as the main longitudinal reinforcement. In addition, these beam forms suffer from a low stiffness which renders its deformation, instead of its load capacity, the critical concern in design, and poor ductility due to the brittle nature of FRP materials.

BRIEF SUMMARY OF THE INVENTION

The purpose of the invention is to provide a novel hybrid FRP-concrete-steel double-skin tubular beam and a hybrid beam/slab unit which employs the hybrid tubular beam to address the aforementioned drawbacks in the prior art.

The technical solution that the invention proposes is a hybrid double-skin tubular beam, wherein the hybrid double-skin tubular beam consists of an outer FRP tube, an inner steel tube, and concrete filled between the outer FRP tube and the inner steel tube, and the inner steel tube is provided with a plurality of shear connectors on its side engaged with concrete so as to ensure the inner steel tube and the concrete to work together.

In an embodiment according to the invention, the plurality of shear connectors are distributed along the circumferential and longitudinal directions of the inner steel tube.

In an embodiment according to the invention, the inner steel tube is located eccentrically relative to the outer FRP tube towards the side of the hybrid tubular beam to be tensed.

In an embodiment according to the invention, the cross sectional shape of the hybrid double-skin tubular beam is an arbitrary combination of an outer FRP tube of circular, square, rectangular or any other suitable shapes and an inner steel tube of circular, square, rectangular or any other suitable shapes. In an embodiment, the cross sectional shape of the hybrid double-skin tubular beam is identical along the longitudinal direction. Alternatively, the inner steel tube is located inclinedly relative to the outer FRP tube along the longitudinal direction in such a way that the inner steel tube is closer to the lower portion of the cross section in the region of positive bending moments and is closer to the upper portion of the cross section in the region of negative bending moments.

In an embodiment according to the invention, the outer FRP tube may be manufactured by means of a winding moulding process. The orientation of the fibers of the outer FRP tube may be customized according to structural requirements. In most applications, fibers are mainly wound along the circumferential direction or substantially along the circumferential direction.

The invention additionally proposes a hybrid DSTB/slab unit which is comprised of a beam and a slab provided thereon, wherein the beam is a hybrid double-skin tubular beam, including an outer FRP tube, an inner steel tube and concrete filled therebetween; and the inner steel tube is provided with a plurality of shear connectors on its side engaged with concrete to ensure the inner steel tube to work together with the concrete.

The invention further proposes a hybrid DSTB/slab unit which consists of a hybrid double-skin tubular beam and an FRP-rib reinforced concrete slab, wherein the upper portion of the hybrid double-skin tubular beam is engaged with the bottom of the FRP-rib reinforced concrete slab thereinside so as to form an integrated body; the hybrid double-skin tubular beam is comprised of an outer FRP tube, an inner steel tube and concrete filled therebetween; and the inner steel tube is provided with a plurality of shear connectors on its side engaged with concrete to ensure the inner steel tube to work together with the concrete.

In the embodiment according to the invention, the hybrid double-skin tubular beam is embedded with a reinforcement rib in the upper portion thereof; the reinforcement rib penetrates through the outer FRP tube, and is connected with the bottom FRP ribs of the FRP-rib reinforced concrete slab so as to integrate the hybrid double-skin tubular beam and the FRP-rib reinforced concrete slab.

Compared with RC beams and steel beams, the hybrid FRP-concrete steel double-skin tubular beams (DSTBs) according to the invention have a main advantage of excellent corrosion resistance. Compared with types I to IV beams, the advantages of hybrid DSTBs lie in: (1) cost effectiveness because of the use of less FRP material (only a thin outer FRP tube is needed); (2) excellent ductile behavior as the inner steel tube acts as the ductile longitudinal reinforcement. Besides the above two advantages, hybrid DSTBs allow for easier connection to other members than type I beams due to the presence of the inner steel tube and concrete. In addition, the outer FRP tube of the hybrid double-skin tubular beam provides good confinement to the compressive concrete, which is not provided by type II and III beams. Furthermore, the hybrid double-skin tubular beam is lighter than type II and IV beams due to the elimination of redundant tensile concrete.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter the invention will be further described with reference to the embodiments and the accompanying figures, wherein,

FIG. 1 illustrates the cross sectional structure of the first embodiment of the hybrid double-skin tubular beam according to the invention.

FIG. 2 illustrates the cross sectional structure of the second embodiment of the hybrid double-skin tubular beam according to the invention.

FIG. 3 illustrates the cross sectional structure of the third embodiment of the hybrid double-skin tubular beam according to the invention.

FIG. 4 illustrates the cross sectional structure of the first embodiment of the hybrid DSTB/slab unit according to the invention.

FIG. 5 illustrates the cross sectional structure of the second embodiment of the hybrid DSTB/slab unit according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

To clarify the purpose, the technical solutions and the advantages of the invention, the invention will be further described with reference to the accompanying figures and embodiments. It should be appreciated that the embodiments illustrated herein are intended to explain the invention, and will not limit the scope of the invention by any means.

FIG. 1 depicts the cross sectional structure of the first embodiment of the hybrid double-skin tubular beam 10 according to the invention. As shown in FIG. 1, the hybrid double-skin tubular beam 10 is a beam form in the shape of a hollow cylinder, consisting of a circular outer tube 11 made of fiber-reinforced polymer, a circular inner tube 12 made of steel, and concrete 13 filled between the outer tube 11 and the inner tube 12. The outer FRP tube 11 and the inner steel tube 12 are not deployed coaxially in such a way that the inner steel tube 12 shifts a distance towards the side of the hybrid tubular beam 10 that would be tensed. As such, the steel tube can be fully exploited to behave as a material to be longitudinally tensed due to its good ductility. Furthermore, the inner steel tube 12 is provided with a plurality of shear connectors 14 on its side engaged with concrete, which not only ensure the composite action between the inner steel tube 12 and the concrete 13, but also act as positioning spacers between the outer FRP tube 11 and the inner steel tube 12 so as to fix the relative location therebetween. In the embodiment as shown in FIG. 1, the shear connectors 14 are distributed evenly along the circumferential direction and the longitudinal direction (not shown in the figure) of the inner tube 12. The shear connectors 14 may take a form of a T-shaped rib, a stud, or any other suitable structure, and may be fixed on the side of the inner steel tube 12 via welding or any other means. The depth that the shear connector embeds into the concrete 13 is determined according to the thickness of the concrete 13 at the corresponding location and the load requirement of the structure. It is obvious that the invention is not limited thereto, and the shape and the distribution of the shear connectors may vary in accordance with specific applications in various embodiments.

FIG. 2 depicts the cross sectional structure of the hybrid double-skin tubular beam 20 according to the second embodiment of the invention. The hybrid double-skin tubular beam 20 is a beam form in the shape of a hollow rectangular column. Its structure is similar to that of the hybrid double-skin tubular beam 10. As particularly shown in FIG. 2, the hybrid double-skin tubular beam 20 consists of a rectangular outer FRP tube 21, a circular inner steel tube 22, and concrete 23 filled between the outer tube 21 and the inner tube 22. Similarly, the inner steel tube 22 shifts, with respect to the outer FRP tube 21, a distance towards the side of the hybrid tubular beam 20 that would be tensed. As such, the steel tube can be fully exploited to behave as a material to be longitudinally tensed due to its good ductility. Furthermore, the inner steel tube 22 is circumferentially provided with a plurality of shear connectors 24 on its side engaged with concrete, which, on the one hand, ensure the composite action between the inner steel tube 22 and the concrete 23, and on the other hand, act as positioning spacers between the outer FRP tube 21 and the inner steel tube 22 so as to fix the relative location therebetween.

FIG. 3 depicts the cross sectional structure of the hybrid double-skin tubular beam 30 according to of the third embodiment of the invention. The hybrid double-skin tubular beam 30 is a beam form in the shape of a hollow rectangular column. Its structure is similar to those of the hybrid double-skin tubular beam 10 as shown in FIG. 1 and the hybrid double-skin tubular beam 20 as shown in FIG. 2. As particularly shown in FIG. 3, the hybrid double-skin tubular beam 30 consists of a rectangular outer FRP tube 31, a rectangular inner steel tube 32, and concrete 33 filled between the outer tube 31 and the inner tube 32. Similarly, the inner steel tube 32 shifts, with respect to the outer FRP tube 31, a distance towards the side of the hybrid tubular beam 30 that would be tensed. As such, the steel tube can be fully exploited to behave as a material to be longitudinally tensed due to its good ductility. Furthermore, the inner steel tube 32 is circumferentially provided with a plurality of shear connectors 34 on its side engaged with concrete, which, on the one hand, ensure the composite action between the inner steel tube 32 and the concrete 33, and on the other hand, act as positioning spacers between the outer FRP tube 31 and the inner steel tube 32 so as to fix the relative location therebetween.

Even though various embodiments of the hybrid double-skin tubular beam that have different cross sectional shapes are hereinbefore described with reference to FIGS. 1-3, it is obvious that the invention is not limited thereto. For example, the cross sectional shape of the hybrid double-skin tubular beam may be an arbitrary combination of an outer FRP tube of circular, square, rectangular or any other suitable shapes and an inner steel tube of circular, square, rectangular or any other suitable shapes.

In the hybrid double-skin tubular beam according to the invention, the outer FRP tube offers mechanical resistance primarily in the circumferential direction, and mainly functions to confine the concrete and to enhance the shear resistance of the beam. Only a low level of mechanical resistance of the outer FRP tube is needed in the longitudinal direction to support wet concrete when in-situ casting is used and to avoid undesirable tensile cracking under service loading. This characteristic of the hybrid double-skin tubular beam features two advantages. Firstly the FRP tube may be very thin such that the material cost may be reduced; and secondly, the concrete is confined and the ductility of the beam is enhanced. Such outer FRP tube may be manufactured by means of fiber-winding moulding process in which fibers are wound substantially along the circumferential direction (e.g. ±80°). In such a way the shear resistance of the hybrid tubular beam is enhanced and the confinement imposed on the concrete is ensured.

The predominant advantage of the hybrid double-skin tubular beam according to the invention is excellent corrosion resistance since the outer FRP per se features an excellent corrosion resistance and the inner steel tube is protected by the outer FRP tube and the concrete from corrosion. If necessary, the both ends of the inner steel tube may be welded with steel plate so as to seal the hybrid tubular beam. Among others, the hybrid double-skin tubular beam according to the invention possesses the following advantages. Its ductility is excellent since the inner steel tube with good ductility is employed as the material to bear longitudinal tension and the concrete is appropriately confined by the inner and outer tubes. The hybrid tubular beam is lightweight since a large amount of concrete under tension may be dispensed with due to the hollow configuration of the cross section. The inner tube and the outer tube may function as the permanent dies for casting concrete such that the hybrid tubular beam is easy for construction. The hybrid tubular beam allows for easier connection to other members due to the presence of the inner steel tube and the concrete. In addition, employment of the inner steel tube ensures that the hybrid tubular beam features a high resistance against bending, such that the main drawback associated with the prior art glass fiber FRP bar-reinforced concrete beams that the excessive flexibility (instead of strength) becomes the critical design consideration due to relatively low elastic modulus is overcome.

The hybrid double-skin tubular beam according to the invention is cost-effective even considered for initial constructions. The fibers in the outer FRP tube mainly take tension due to the fact that the outer FRP tube primarily serves as the protective layer against corrosion, the permanent die for concrete casting and the outer shell for enhancing shear resistance and ductility. Therefore relatively thin FRP tube may fulfill these purposes. In this way, the cost of the thin outer FRP tube and the inner steel tube can be entirely compensated by labor and/or material costs saved by dispensing with excessive concrete under tension, temporary dies and steel bars. Therefore, the initial construction cost of the hybrid double-skin tubular beam according to the invention is comparable to that of the prior art reinforced concrete. In addition, since the former is lighter, the cost of the supports will be further reduced. Finally the maintenance cost will be greatly reduced due to excellence corrosion resistance of the hybrid double-skin tubular beam according to the invention.

Hereinbefore, the hybrid double-skin tubular beams with identical cross sections along the longitudinal direction are described with reference to the embodiments as illustrated in FIGS. 1-3. These hybrid tubular beams are particularly suitable to be employed as simply supported beams. In other embodiments of the invention, the inner steel tube may be provided inclinedly along the longitudinal direction in such a way that the inner steel tube is closer to the lower portion of the cross section in the region of positive bending moments and is closer to the upper portion of the cross section in the region of negative bending moments. Such hybrid double-skin tubular beams may be used as continuous beams.

The hybrid double-skin tubular beams according to the invention can be employed as bridge girders, bridge girder/slab components, and flexural members (e.g. beams and slabs) in other structures in a corrosive/harsh environment. Hereinafter, the applications of the hybrid double-skin tubular beams according to the invention in hybrid beam/slab units will be described with reference to FIGS. 4-5.

FIG. 4 illustrates the cross sectional structure of the first embodiment of the hybrid beam/slab unit according to the invention. As shown in FIG. 4, the hybrid beam/slab unit 40 consists of a hybrid double-skin tubular beam 41 according to the embodiment of the invention and a slab 42 provided thereon, resulting in a slab-on-girder bridge system, wherein the hybrid double-skin tubular beam 41 is a beam form with a hollow rectangular cross section as depicted in FIG. 2. As particularly shown in FIG. 4, the hybrid double-skin tubular beam 41 consists of a rectangular outer FRP tube 411, a circular inner steel tube 412 and concrete 413 filled therebetween. The inner steel tube 412 is provided with a plurality of shear connectors 414 on its side engaged with concrete to ensure the composite action between the inner steel tube 412 and the concrete 413. The slab 42 may be manufactured from FRP composite materials, aluminum or other lightweight materials of high resistance against corrosion. The slab 42 may also be a hybrid FRP-concrete slab, e.g., a hybrid slab resulting from casting a concrete layer on a FRP profile. The slab 42 may be cohered to the hybrid double-skin tubular beams 41 via an adhesive layer 43. Alternatively, the hybrid double-skin tubular beams 41 and the slab 42 may be connected via couplers (such as shear connectors).

FIG. 5 illustrates the cross sectional structure of the second embodiment of the hybrid beam/slab unit according to the invention. As shown in FIG. 5, the hybrid beam/slab unit 50 consists of a hybrid double-skin tubular beam 51 according to the embodiments of the invention and an FRP-rib reinforced concrete slab 52, resulting in a bridge deck or floor system, The FRP-rib reinforced concrete slab 52 is provided with a plurality of FRP ribs, such as the FRP ribs 521, 522 as shown and unshown longitudinal ribs located on the bottom of the slab 52 to control cracks. The hybrid double-skin tubular beam 51 is a beam form with a hollow cylindrical cross section similar to the embodiment as depicted in FIG. 1. The hybrid double-skin tubular beams consists of a circular outer FRP tube 511, a circular inner steel tube 512 and concrete 513 filled therebetween. The inner steel tube 512 is provided with a plurality of first shear connectors 514 on its side engaged with concrete to ensure the composite action between the inner steel tube 512 and the concrete 513. In addition, the hybrid tubular team 51 is pre-embedded with a reinforcement rib 515 in the upper portion thereof. The reinforcement rib 515 penetrates through the wall of the outer FRP tube 511, and is connected via mechanical couplers 523 with the bottom FRP ribs 521 of the concrete slab 52 so as to integrate the hybrid tubular beam 51 and the concrete slab 52. Furthermore, if necessary, the hybrid tubular beam 51 may be provided with second shear connectors 516 of any other suitable form. The second shear connecter 516 penetrates through the outer FRP tube 611 and is embedded into concrete slab 52 so as to ensure composite action between the hybrid tubular beam 51 and the concrete slab 52. The reinforcement rib 515 and the second shear connectors 516 may be made from stainless steel, steel with polymer coating, or any other materials with excellent resistance against corrosion. Since all the fibers of the outer FRP tube 511 are wound substantially along the circumferential direction, penetration of the reinforcement rib 515 and the second shear connectors 516 through the out FRP tube 511 will not evidently affect the overall performance of the out tube. Therefore, the hybrid beam/slab unit 50 inherits all advantages of the aforementioned hybrid double-skin tubular beam.

The hybrid DSTBs and hybrid DSTB/slab units employing the DSTBs according to the invention are competitive alternatives to existing beam forms and bridge deck/floor systems. The invention provides a durable, ductile and cost-effective solution to help overcome the worldwide infrastructure deterioration problem.

Although preferred embodiments of the invention have been described and illustrated herein, it is recognized that modifications, alternatives and variations may readily occur to those skilled in the art and, consequently, it is intended that the claims be interpreted to cover such modifications and equivalents. 

1. A hybrid double-skin tubular beam, characterized in that, the hybrid double-skin tubular beam consists of an outer FRP tube, an inner steel tube, and concrete filled between the outer FRP tube and the inner steel tube, and the inner steel tube is provided with a plurality of shear connectors on its side engaged with concrete so as to ensure the inner steel tube and the concrete to work together.
 2. The hybrid double-skin tubular beam as claimed in claim 1, characterized in that, the plurality of shear connectors are distributed along the circumferential and longitudinal directions of the inner steel tube.
 3. The hybrid double-skin tubular beam as claimed in claim 1, characterized in that, the inner steel tube is located eccentrically relative to the outer FRP tube towards the side of the hybrid tubular beam to be tensed.
 4. The hybrid double-skin tubular beam as claimed in claim 1, characterized in that, the cross sectional shape of the hybrid double-skin tubular beam is an arbitrary combination of an outer FRP tube of circular, square, rectangular or any other suitable shapes and an inner steel tube of circular, square, rectangular or any other suitable shapes.
 5. The hybrid double-skin tubular beam as claimed in claim 4, characterized in that, the cross sectional shape of the hybrid double-skin tubular beam is identical along the longitudinal direction.
 6. The hybrid double-skin tubular beam as claimed in claim 4, characterized in that, the inner steel tube is located inclinedly relative to the outer FRP tube along the longitudinal direction in such a way that the inner steel tube is closer to the lower portion of the cross section in the region of positive bending moments and is closer to the upper portion of the cross section in the region of negative bending moments.
 7. The hybrid double-skin tubular beam as claimed in claim 1, characterized in that, the outer FRP tube is manufactured by means of a winding moulding process, and fibers of the outer FRP tube are mainly wound along the circumferential direction or substantially along the circumferential direction.
 8. A hybrid beam/slab unit, which consists of a beam and a slab provided thereon, characterized in that, the beam is a hybrid double-skin tubular beam, including an outer FRP tube, an inner steel tube and concrete filled therebetween; and the inner steel tube is provided with a plurality of shear connectors on its side engaged with concrete to ensure the inner steel tube to work together with the concrete.
 9. A hybrid beam/slab unit, characterized in that, the hybrid unit consists of a hybrid double-skin tubular beam and an FRP-rib reinforced concrete slab; the upper portion of the hybrid double-skin tubular beam is engaged with the bottom of the FRP-rib reinforced concrete slab thereinside so as to form an integrated body; the hybrid double-skin tubular beam is comprised of an outer FRP tube, an inner steel tube and concrete filled therebetween; and the inner steel tube is provided with a plurality of shear connectors on its side engaged with concrete to ensure the inner steel tube to work together with the concrete.
 10. The hybrid beam/slab unit as claimed in claim 9, characterized in that, the hybrid double-skin tubular beam is embedded with a reinforcement rib in the upper portion thereof; the reinforcement rib penetrates through the outer FRP tube, and is connected with the bottom FRP ribs of the FRP-rib reinforced concrete slab so as to integrate the hybrid double-skin tubular beam and the FRP-rib reinforced concrete slab. 